Accelerators for refractory magnesia

ABSTRACT

The hardening of a composition containing a phenolic resin solution and a magnesia aggregate is effected by mixing into such composition at a pH of at least 4.5: a compound which provides an acetate, adipate, 4-aminobenzenesulfonate, 1,2,4-benzenetricarboxylate, formate, glycolate, lactate, nitrate, benzenesulfonate, naphthalenesulfonate, methanesulfonate, phenolsulfonate, succinate, sulfamate, or toluenesulfonate anion to the composition; or an acetylacetone, 2-nitrophenol, 4-nitrophenol, salicylaldehyde compound; or a mixture of said compounds.

This application is a divisional application of my copending applicationSer. No. 07/943,046 filed on Sep. 10, 1992, now U.S. Pat. No. 5,218,010,which in turn is a divisional of my application Ser. No. 07/803,979filed on Dec. 9, 1991, now U.S. Pat. No. 5,182,347, which is in turn isa continuation-in-part of my application Ser. No. 07/616,879 filed onNov. 21, 1990, now U.S. Pat. No. 5,182,346, and which in turn is acontinuation-in-part of Ser. No. 07/562,206 filed on Aug. 2, 1990, nowU.S. Pat. No. 5,096,983 which issued on Mar. 17, 1992.

This application is also related to my copending application Ser. No.07/748,707 which was filed on Aug. 22, 1991 and which is directed toretarders for hardening a phenolic resin and magnesia aggregate.

BACKGROUND OF THE INVENTION

This invention relates to methods and compositions useful in themanufacture and use of ceramic and refractory compositions. Moreparticularly this invention relates to methods and compositions foraccelerating the hardening of compositions containing hardburnedmagnesia or deadburned magnesia, both of which are simply referred toherein as "magnesia aggregate", and a curable phenolic resin, with orwithout the inclusion of an ester functional hardening agent. Theacceleration in hardening is accomplished by incorporating in thecompositions certain compounds, such as those which supply: acetate;adipate; 1,2,4-benzenetricarboxylate (trimellitate); formate; glycolate;lactate; nitrate; succinate; sulfamate; phenolsulfonate; ortoluenesulfonate anions to the composition; an acetylacetone(2,4-pentanedione); 2-nitrophenol; 4-nitrophenol; or salicylaldehydecompound; or a mixture of compounds which supply said anions orcompounds.

It is often desirable to accelerate or shorten the time it takes forphenolic resins to harden a magnesia aggregate. This is particularly thecase in cooler climates and at lower temperatures. Accelerators are alsoadvantageous for reducing the strip time of molded or cast materials.The methods and compositions of this invention accomplish suchacceleration in hardening.

DESCRIPTION OF THE RELATED ART

U.S. Pat. Nos.: 2,424,787 to W. Adams, Jr. of Jul. 29, 1947; 2,869,191to R. Cooper et al. of Jan. 20, 1959; 2,869,194 to R. Cooper of Jan. 20,1959; 2,869,196 to Cooper of Jan. 20, 1959; 2,913,787 to Cooper of Nov.24, 1959 and 3,666,703 to T. Murata et al. of May. 30, 1972 relate tothe use of alkali metal or alkaline earth metal oxides to hardenphenolic resins.

U.S. Pat. No. 4,794,051 to Gupta of Dec. 27, 1988 and Jpn. Kokai TokkyoKoho JP 60/90251 of May 21, 1985 are directed to hardening of certainphenolic resins in the presence of a magnesium oxide and esterfunctional hardening agent.

U.S. Pat. No. 4,831,067 to P. Lemon et al. of May 16, 1989; 4,939,188 toA. Gerber of Jul 3, 1990; Re 32,720 to P. Lemon et al. of Jul. 26, 1988;Re 32,812 to P. Lemon et al. of Dec. 27, 1988; and PCT/GB89/01526 to P.Lemon et al. of Dec. 21, 1989 disclose the use of ester functionalhardening agents for the room temperature hardening of phenolic resins.

U.S. Pat. No. 4,740,535 to R. Iyer et al. of Apr. 26, 1988 discloses themanufacture of a modified phenolic resole resin and compositions usingsuch resin in the foundry and refractory arts. That patent alsodiscloses curing such resin under highly acidic conditions with acidssuch as toluenesulfonic acid at ambient temperatures or by thermalcuring. The use of various aggregates, including magnesia, are recitedin the reference. Differences of this reference from the instantinvention include the absence of highly acidic conditions for hardeningthe resin in the instant invention.

Additionally, U.S. Pat. No. 2,712,533 to J. Mitchell of Jul. 5, 1955discloses compositions comprising a novolac resin and magnesium oxide;U.S. Pat. No. 4,282,288 to Yoshino et al. of Aug. 4, 1981 disclosesrefractory compositions containing a powdered phenolic resin andadditives such as magnesia and phosphates; U.S. Pat. No. 4,964,917 to G.Bobrowski et al. of Oct. 23, 1990 discloses a method for retarding thehydration of concrete by addition of a chelating agent for calcium andeventually adding an accelerator to harden the composition; U.S. Pat.No. 4,473,654 to J. Stenders of Sep. 25, 1984 relates to binding ofrefractory aggregates with various binding agents; U.S. Pat. No.4,539,343 to T. Nishimura of Sep. 3, 1985 discloses the use of variousadditives to eliminate reddish color in mixtures of magnesia containingcompositions and a phenolic resin; and U.S. Pat. No. 4,961,795 toDetlefsen et al. of Oct. 9, 1990 shows the use of aliphatic alcohols tomoderate or retard the hardening of phenolic resins with esterfunctional hardening agents.

European Patent Application 0202004 to Foseco International Limitedwhich was published on Nov. 20, 1986 discloses refractory compositionsof deadburned magnesite, a dispersing agent such as sodium alkylsulfate, an ester functional hardening agent and a phenol formaldehyderesin.

Abstract of Soviet Union patent publication SU 1316994 of 870615 to K.Simonov et al. relates to magnesia aggregate refractories bound withphenolic resin and chloride and bromide salt additives.

Abstract of Japanese patent publication JP 57051176 dated 820385 whichis assigned to Kawasaki Steel KK of 820318 relates to a refractorycomposition comprising a phenolic resin, fireproof aggregate andadditives such as magnesium sulfate.

SUMMARY OF THE INVENTION

It has been found that the ambient temperature hardening of compositionscontaining magnesia aggregate and a curable, liquid phenolic resin,either alone or together with an ester functional hardening agent, canbe accelerated by the use of certain additives. Such acceleratoradditives include: those which supply: acetate; adipate;1,2,4-benzenetricarboxylate (trimellitate); formate; glycolate; lactate;nitrate; succinate; sulfamate; phenolsulfonate; or toluenesulfonateanions to the composition or compounds which supply acetylacetone(2,4-pentanedione); 2-nitrophenol; 4-nitrophenol; or salicylaldehyde tothe composition.

The compositions of this invention are useful in the preparation ofceramics and various refractories such as shaped articles, e.g., bricksand castable monolithic shapes as well as refractory tile and the like.

In one aspect of the invention, a binder-aggregate composition isprovided. The binder-aggregate comprises a mixture of: (a) magnesiaaggregate; (b) a curable phenolic resin solution wherein the resin ispresent in sufficient quantity to harden or decrease the flow of themixture on standing at ambient temperature; (c) an accelerator of thisinvention; and (d) optionally, an ester functional hardening agent andconventional additives used in refractory and ceramic compositions. Suchcompositions have a pH of at least 4.5 and, as the composition ages andbecomes more viscous, the pH will increase such as that of 7 to 10 orhigher. The resin is present in sufficient quantity to bind theaggregate on thermal curing of the resin.

In another aspect, the invention involves a method for making abinder-aggregate composition which comprises mixing the ingredients usedin the above mentioned binder-aggregate composition. Preferably, themixing produces a composition which is wet and shapable.

In still another aspect, a binder-aggregate composition of thisinvention containing a phenolic resole resin together with the magnesiaaggregate and accelerator is formed into a desired shaped article, andthe article can be allowed to stand at ambient temperature to developthe requisite ambient temperature strength which is also referred to asgreen strength

Still further aspects of the invention involve thermal curing of theshaped article and optionally heating at a still higher temperature tocarbonize the resin binder to form a refractory body.

DETAILED DESCRIPTION OF THE INVENTION The Phenolic Resin

The phenolic resin can be a novolac solution, a resole solution, anovolac in a resole solution or a mixture of the foregoing.

The phenolic resole resin solutions which may be used in this inventioncan be that of phenol formaldehyde or those wherein phenol is partiallyor completely substituted by one or more phenolic compounds such ascresol, resorcinol, 3,5-xylenol, bisphenol-A, or other substitutedphenols and the aldehyde portion can be partially replaced by a phenolreactive aldehyde such as acetaldehyde, furaldehyde or benzaldehyde.

Resole resins are thermosetting, i.e., they form an infusible threedimensional polymer upon application of heat and are produced by thereaction of a phenol and a molar excess of a phenol-reactive aldehydetypically in the presence of an alkali or alkaline earth metal compoundas condensing catalyst at a pH above 7. Typically, the resole resin willbe a phenol-formaldehyde resin produced by reacting phenol andformaldehyde in a molar ratio (phenol: formaldehyde) within the range offrom about 1:1 to 1:3. A preferred molar ratio for use in this inventionranges from about one mole of the phenol for each mole of the aldehydeto about 1 mole of phenol for 2.2 moles of the aldehyde and particularlya range of phenol to aldehyde of 1 to 1.2 to 1 to 2. The phenolic resoleresin will usually be in aqueous solution. Preferred phenolic resoleresins used in this invention have less than about 1% and preferably notmore than 0.5% by weight of soluble sodium or potassium.

Resoles can be prepared with a variety of condensation catalysts. Theseinclude alkali and alkaline earth oxides and hydroxides, quaternaryammonium hydroxides, as well as ammonia and organic amines. It ispreferable to have the accelerator fully soluble and stable in thephenolic resin. In such case, particularly where the phenolic is aresole solution, the phenolic resin and the accelerator canadvantageously be placed in storage. A less desirable system is whereina portion of the accelerator is uniformly dispersed as a fine powder inthe phenolic solution. Least desirable is when a portion of theaccelerator forms a precipitate which settles out upon storage.

The pH of the phenolic resole resin used in this invention willgenerally vary from about 4.5 to 9.5 with a pH of 5 to 8.5 beingpreferred. The molecular weight of the resin will vary from about 200 to3,000 weight average molecular weight with 300 to 1,000 being preferred.All other things being equal, higher molecular weights and lowerfree-phenol content will provide shorter ambient temperature gel orhardening time and increase strength development with resole resins. Theweight average molecular weight is measured using gel permeationchromatography and phenolic compounds and polystyrene standards. Thesample molecular weight to be measured is prepared as follows: the resinsample is dissolved in tetrahydrofuran and slightly acidified with 1Nhydrochloric or sulfuric acid and dried over anhydrous sodium sulfate.The salts which result are removed by filtration and the supernatantliquid run through a gel permeation chromatograph.

The resin solids in the resole resin solution can vary over a broadrange such as that of about 50% to 90% by weight of the phenolic resoleresin. Preferably, the resin solids vary from about 50% to 80% by weightof the phenolic resole resin. The viscosity of the resin can vary over abroad range such as that of from about 100 to 10,000 cps at 25° C.Preferably, the viscosity varies from about 250 to 5,000 cps at 25° C.The viscosity measurements herein are given in centipoise (cps) asmeasured by a Brookfield RVF viscometer at 25.C or by Gardner-Holtviscosities at 25° C. The Gardner-Holt viscosities which are incentistokes are multiplied by the specific gravity (generally 1.2) togive the cps at 25° C.

The quantity of free phenol in the resole resin can vary over a broadrange such as from about 5% to 15% based on the weight of the resin(BOR). Increasing the quantity of free phenol increases the roomtemperature mix life of the hardenable binder-aggregate composition.

The liquid portion of the resole resin is water or water together withfree phenol and optionally a non-reactive solvent. Solvents in additionto water can be selected from alcohols of one to five carbon atoms,diacetone alcohol, glycols of 2 to 6 carbon atoms, mono- and dimethyl orbutyl ethers of glycols, low molecular weight (200- 600) polyethyleneglycols and methyl ethers thereof, phenolics of 6 to 15 carbons,phenoxyethanol, butyl acetate, propylene glycol, dipropylene glycol,methyl ethyl ketone, methyl isobutyl ketone, cyclic ethers such astetrahydrofuran and m-dioxolane, and the like.

Typical water contents of the resole resins used in this invention willvary from about 3% to 20% by weight (BOR). Preferably the water contentof the resole resin is from about 3% to 15% BOR (based on the weight ofresin). Apart from water in the resin as manufactured, additional watercan be mixed into the resin itself or the binder-aggregate composition.Preferably the total water content of the binder-aggregate compositionvaries from about 0.5% to 5% by weight. Increasing the water content ofthe resin or total water in the binder-aggregate composition decreasesthe ambient temperature mix life of the binder-aggregate composition.

The Novolac Resin

The novolac resin can be used as a liquid solution when used alone asthe phenolic resin or as a liquid or solid when used together with aresole solution.

For use in this invention, the novolac will have a molecular weight ofabout 300 to 3,500. Solvents which can be used for dissolving thenovolac include: ethylene glycol; furfuryl alcohol, diacetone alcohol,glycol ether acetate; glycol ether; and mixtures thereof as well aslower alcohols, e.g., methanol, ethanol, 1- and 2-propanol, 1-butanoland the like. Preferred novolac solids content will be from about 50% to70% by weight of the novolac solution. Preferred viscosities for thenovolac solutions are from about 2,000 to 6,000 cps at 25° C. However,ground or powdered novolac can be added to a resole solution for formingthe binder-aggregate composition.

A novolac resin is one prepared with a deficiency in aldehyde so thatwhen used alone, it is normally not curable unless a curing agent suchas hexamethylenetetraamine ("hexa") is added together with heat for athermal cure. A novolac resin may be defined as the generally acidicresinous reaction product of a phenolic material and an aldehyde that,for practical purposes, does not harden or convert to an insoluble,infusible condition upon heating but remains soluble and fusible.

By "novolac" herein is meant novolac resins, polymers, copolymers,terpolymers or mixtures comprising a phenolic material such as phenol,cresol, or xylenol or mixtures thereof reacted with formaldehyde orother commercially used reactants for production of novolacs such asbenzaldehyde, furaldehyde, acetaldehyde and acetone. The formaldehyde:phenolic mole ratio of the novolacs useful in the present invention isin the range of about 0.5:1 to about 0.9:1, and preferably about 0.6:1to 0.8:1, wherein the phenolic material is selected from phenol, o-,m-,and p-cresol, xylenols and mixtures thereof. Preferably, the novolacresin is prepared by condensing formaldehyde and phenol at a pH of lessthan about 4, and more preferably about 2.

Hexa and/or other methylene-generators, such as for example formaldehydeor paraformaldehyde, can be added to the novolac containing binders ofthe present invention. When used, hexa is added at a level of about 4%to about 15%, based on the weight of total novolac phenolic resin andmore preferably at about 5% to about 10%. However, the novolac can alsobe cured in the presence of a resole since resoles use higher moleratios of formaldehyde to provide excess methylol groups, some of whichin turn can react with the novolac. When the binder-magnesia aggregatedoes not contain a resole it is preferred that the quantity of calciumoxide in the magnesia aggregate be from 1.5 to 4% by weight of themagnesia aggregate since the rate of hardening of the binder-aggregateincreases with increased calcium oxide content.

The compositions of this invention can utilize a blend of novolac andresole components. By "component" herein is meant an individual resin ofa blend, mixture, reaction product , or other combination of resinscontaining the novolac or resole of reference. Such resin binders alsohave the desirable properties of low thermal conductivity and highdimensional stability and abrasion resistance. When the hardenable(curable) composition contains both a resole and novolac binder, it ispreferred that there be about 1 to 4 parts of resole by weight for eachpart of novolac. In such case it is also preferred that powdered novolacbe added to the resole resin or binder-aggregate mixture.

The quantity of resin used in the binder-aggregate mixture is that whichis sufficient to bind the aggregate on ambient temperature hardening inthe case of a resole or to decrease the flowability of the mixture inthe case a novolac is used alone at ambient temperature or to bind themixture on thermal curing in the case the phenolic is a resole, anovolac or mixtures thereof Thus, the quantity of resin based onaggregate in the binder-aggregate mixture can vary over a broad rangesuch as from about 3% to 15% by weight of resin based on the weight ofthe magnesia aggregate and particularly from about 3% to 8% of resinbased on the weight of magnesia aggregate. As used in this invention,"resoles" are solutions of the phenolic involved even though furtherreferred to as "solutions" whereas "novolacs" are solids.

The Magnesia Aggregate

The magnesia aggregate can be either deadburned magnesia or hardburnedmagnesia. The hardburned and deadburned magnesia aggregates are simplyalso referred to herein as magnesia aggregate. Deadburned magnesia isalso referred to as deadburned magnesite, refractory magnesia orpericlase. To the refractories art, the terms "deadburned magnesite" or"deadburned magnesia" are used interchangeably to describe the dense,highly crystalline, periclase product of good stability, which is usedto fabricate refractory brick and the like. Such magnesia products canbe obtained from the Martin Marietta Magnesia Specialties Company underthe designator of MagChem Magnesium Oxide Products.

Reactivity and surface area of magnesium oxide (magnesia) differ greatlydepending on the procedure used for manufacture of the magnesia. Thesemagnesia products are made by calcining magnesite (MgCO₃) or suchmagnesium compounds as the hydrate, or chloride at differenttemperatures. Lightburned grades of magnesium oxide are prepared bycalcining at temperatures ranging from about 1600° F. to about 1800° F.(871° C. to 982° C.). Hardburned and deadburned magnesia aggregates areprepared by calcining at substantially higher temperatures. Thus,hardburned and deadburned magnesia aggregates are prepared by calciningat temperatures of 2800° F. (1540° C.) and above. In one reference,namely Kirk-Othmer, Encyclopedia of Chemical Technology (John Wiley &Sons, N.Y., 1982) Vol 20 page 8 under the section on Refractories, bothhardburned and deadburned magnesia aggregate appears to be treated thesame since that reference states that deadburned magnesite is obtainedby firing naturally occurring magnesium carbonate at 1540° C. to 2000°C. However, for the purposes of this application, the calciningtemperatures set forth in a brochure of Martin Marietta MagnesiaSpecialties Company entitled MagChem© Magnesium Oxide Grades and Useswill be employed wherein it states that hardburned grades are preparedby calcining at temperatures ranging from about 2800° F. to 3000° F.(1540° to 1649° C.) and that the deadburned grade of magnesium oxide iscalcined at temperatures of over 4000° F. (2204° C.). There are alsodifferences in surface areas for the various magnesias. Thus,lightburned magnesia has a surface area of about 10 to 200 or moresquare meters per gram. Hardburned magnesia and deadburned magnesia havea surface area of about one or less than one square meter per gram.

Commercially available magnesia aggregate commonly analyzes from about91% to over 99% of MgO and preferably 96 to over 99% of MgO with notmore than 4% of CaO by weight as the main impurity and preferably themagnesia aggregate will contain not more than 3.50% of CaO. As thequantity of lime (CaO) increases, the mix life in the binder-magnesiaaggregate decreases. Illustrative of a suitable hardburned magnesiaaggregate there can be mentioned MagChem 10-40 which has a 98.2% MgOcontent on an ignited basis, 0.25% loss on ignition, 0.90% CaO, andsmaller quantities of other oxides with 96% of the product passing a -40U.S. Sieve with a median particle size of 30 microns and a surface areaof less than 1 square meter per gram.

For use in refractory compositions, the magnesia grain is crushed andsized in various fractions. Commonly used grain sizes of deadburned orhardburned grades of magnesia can be used in this invention. A typicalmixture of coarse, intermediate and fine grain fractions of deadburnedmagnesia suitable to achieve high bulk density and low porosity, such asfor use in manufacture of refractory articles useful in basic oxygenprocess furnaces, will ave Tyler standard screen sizes as follows: 30 to35% passing 4 mesh and retained on 10 mesh; 30 to 40% passing a 6 meshand retained on 28 mesh; and 30 to 35% ball mill fines (less than 100mesh). Magnesia aggregate used in this invention preferably containsfrom about 10% to 25% of such aggregate which is ground to a powder.

By the term "room temperature hardening" we mean the hardening ofbinder-aggregate compositions of this invention at temperatures of about60° F. to 90° F., particularly about 65° F. to 80° F. However, the useof accelerators in the processes and compositions of this inventionaccelerate the hardening at lower and higher temperatures such as 60° F.to 110° F., such temperatures being referred to herein as ambienttemperatures. Increase in viscosity with subsequent gelation andhardening of resole resins, even in the absence of magnesia aggregate,at ambient temperatures are the first steps toward curing. Nevertheless,when the novolac is in contact with magnesia aggregate at ambienttemperature, there is a viscosity increase, decreased flow or simplyhardening of the binder-aggregate composition of this invention. Inaddition to hardening at ambient temperature, the binder-aggregatecompositions of this invention can be thermally cured after ambienttemperature hardening or the compositions can be thermally cured priorto such hardening. The term "thermal curing" as used herein means curingof the composition at a temperature of at least 170° F. (77° C.) such asup to 248° F. (120° C.) and generally at a temperature of at least 212°F. (100° C.).

The Ester Hardening Agent

The ester functional hardening agent, when used, further accelerates thehardening of the phenolic resin in the binder-magnesia aggregatecompositions of this invention. The ester functionality can be providedby lactones, cyclic organic carbonates, carboxylic acid esters, ormixtures thereof. Generally, low molecular weight lactones are suitableas the ester functional hardening agent, e.g., beta orgamma-butyrolactone, gamma-valerolactone, caprolactone,beta-propiolactone, beta-butyrolactone, beta-isobutyrolactone,beta-isopentyllactone, gamma-isopentyllactone, and delta-pentyllactone.Examples of suitable cyclic organic carbonates include, but are notlimited to: propylene carbonate; ethylene carbonate; 1,3-butanediolcarbonate; 1,2-pentanediol carbonate; and 1,3-pentanediol carbonate.

The carboxylic acid esters which can be used in this invention includephenolic esters and aliphatic esters. The aliphatic esters arepreferably those of short or medium length, e.g., about 1 to 4 carbonmono- or polyhydric, saturated or unsaturated alcohols with short ormedium chain length, e.g., about 1 to 10 carbon aliphatic, saturated orunsaturated carboxylic acids which can be mono- or polycarboxylic. Thepreferred aliphatic esters are those of alkyl, mono , di-, or trihydricalcohols with alkyl, or mono-, or diunsaturated acids which can be mono,di-, or tricarboxylic.

As to aromatic esters, such esters can be obtained by esterifying thearomatic, e.g., phenolic group or groups of a mono-or polyhydricaromatic phenol to prepare a formate or acetate ester of such aromaticcompound. Additionally, the aromatic ester can be an esterified phenoliccompound containing one or more phenolic hydroxyl groups and/or one ormore esterified phenolic hydroxyl groups and further containing one ormore esterified methylol groups positioned ortho and/or para to aphenolic hydroxyl group or esterified phenolic hydroxy group. Suchphenolic esters and their method of manufacture are disclosed inInternational Application No. PCT/GB89/01526 having a filing date of12/21/89 to Lemon et al.

It will be understood that the esterified phenolic compound used may bea mono-, di- or polynuclear phenol wherein at least one esterifiedmethylol group is attached to an aromatic ring carbon atom ortho or parato a phenolic hydroxyl group or esterified phenolic hydroxyl group. Theacid portion of the phenolic esters can be the same as those of thealiphatic esters.

Specific carboxylic acid esters include but are not limited to: n-butylformate; ethylene glycol diformate; methyl and ethyl lactates;hydroxyethyl acrylate; ethylene glycol diacetate; triacetin (glyceroltriacetate); diethyl fumarate; dimethyl maleate; dimethyl glutarate;dimethyl adipate; 2-acetyloxymethyl phenol; 2-methacryloxymethyl phenol;2-salicyloxylmethyl phenol; 2-acetyloxymethyl phenol acetate;2,6-diacetyloxymethyl p-cresol acetate; 2,4,6- triacetyloxymethylphenol; 2,4,6-triacetyloxymethyl phenol acetate; 2,6-diacetyloxymethylphenol acetate; 2,2',6,6'-tetraacetyloxymethyl bisphenol A diacetate.Also suitable are: cyanoacetates derived from 1 to 5 carbon atomaliphatic alcohols; formates and acetates of benzyl alcohol,alpha,alpha'-dihydroxyxylenols, phenol, alkyl substituted phenols,dihydroxybenzenes, bisphenol A, bisphenol F , and low molecular weightresoles. At times, it is advantageous to use mixtures of the esterfunctional hardening agents.

The ester functional hardening agent is present in an amount sufficientto increase the rate of hardening of such compositions at ambienttemperature and, in the case of resole containing compositions, increasetensile and compressive strength of the ambient temperature hardenedcomposition. The quantity of ester used in the binder aggregatecompositions of this invention will vary over a broad range such as thatof about 5% to 25% by weight of the phenolic resin and preferably fromabout 5% to 15% by weight of the resin. The exact quantity will dependon the particular ester hardener used, the amount and specific magnesiaaggregate used, the temperature at which the composition is used orstored, and desired results.

The ACCELERATORS

The accelerators used in this invention include acetic acid, sodiumacetate, magnesium acetate, calcium acetate, formic acid, ammoniumformate, potassium formate, glycolic acid, sodium glycolate,tetramethylammonium glycolate, lactic acid, sodium lactate, calciumlactate, adipic acid, magnesium adipate, succinic acid, ammoniumsuccinate, 2-nitrophenol, 4-nitrophenol, salicylaldehyde, trimelliticacid (1,2,4-benzenetricarboxylic acid), sulfanilic acid(4-aminobenzenesulfonic acid), sodium sulfanilate, sulfamic acid,benzenesulfonic acid, naphthalenesulfonic acid, methanesulfonic acid,ammonium sulfamate, magnesium sulfamate, phenolsulfonic acid, the sodiumsalt of phenolsulfonic acid, nitric acid, lithium nitrate, potassiumnitrate, acetylacetone (2,4-pentanedione), toluenesulfonic acid, thepotassium salt of toluenesulfonic acid, the ammonium salt ofbenzenesulfonic acid, the ammonium salt of naphthalenesulfonic acid, thesodium salt of methanesulfonic acid, and the like. Additional salts ofthe above mentioned accelerator acids which have some solubility in thephenolic resin are also operable. Such salts include those which have awater solubility of at least 0.1% and preferably at least 2% by weightat 25° C., so that the accelerator compound can provide anions, e.g.,sulfamate, to the compositions. It can be seen that for ionizablecompounds, the accelerator can be in the form of an acid or a salt.

Some of the accelerators are strong acids and care needs to be exercisedto keep the binder-aggregate at a pH of about 4 or above. Otherwise acidcatalysis of the phenolic may take place and prematurely harden thebinder-aggregate composition. When suflanilic acid(4-aminobenzenesulfonic acid) or the sulfanilate anion is theaccelerator, ester hardening agents should be avoided. The reason forthis is that such esters appear to inhibit the accelerating effect ofsulfanilic acid or the sulfanilate anion.

For ionizable compounds, it is the anion, e.g., toluenesulfonate ornitrate, which determines whether these materials are accelerators.Thus, the cation, e.g., Na⁺, H⁺, K⁺ does not change the anion from beingan accelerator although it may have some effect on the amount ofacceleration. Thus, there would normally be less hardening accelerationfor compounds having less solubility in the phenolic resin solution. Inthe case of ionizable accelerator compounds, such compounds provide theaccelerator anions to the composition. For this, some solubility in thecomposition, e.g. binder-aggregate or water, is needed. However, somecompounds which do not appear to readily ionize are also accelerators.Such accelerators include the nitrophenols.

A benefit of using ammonium or an amine salt of an acid is that it ismore soluble than sodium or potassium salts. To prevent too low of a pH,which could lead to acid catalyzed polymerization, partialneutralization by an amine permits higher levels of acid to be used. Thesalts of the accelerator acids are advantageously that of amines.Illustrative of such amines there can be mentioned:N,N-dialkylethanolamines having from 1-3 carbon atoms in each alkylgroup and preferably 1 to 2 carbon atoms; g-and -dialkylaminmethylphenol having from 1 to 2 carbon atoms in each alkyl group;N,N-dimethylbenzylamine; N-alkylpiperidine having from 1 to 2 carbonatoms in each alkyl group; N-methyl or N-ethylmorpholine;N,N,-dimethylethanolamine; N,N,-diethylethanolamine;N,N,-dimethylbenzylamine; and the like. The foregoing amines aretertiary amines. Primary and secondary amines can be used with acidicaccelerators where there is no undue destabilization of resin relativeto the use of a tertiary amine. In any event, primary and secondaryamines should be avoided when an organic ester is in thebinder-aggregate composition as a hardening agent. Illustrative ofprimary and secondary amines for preparing salts of the acidicaccelerators there can be mentioned: ethanolamine and its N-monomethyland its N-monoethyl derivatives; 1- and 2-aminopropanols; N-methylbenzylamine; morpholine; piperidine and diethanolamine.

Preferably, the accelerator anion is combined with hydrogen as thecation or cations and used in the acid form of the accelerator compound,e.g., as in sulfamic acid or glycolic acid. Also preferred cations forcombining with the accelerator anions of this invention are those of thealkali metals, magnesium, calcium, ammonium, and lower alkyl substitutedammonium having from 1 to 4 carbon atoms in each alkyl group.

The quantity of accelerator compound used in this invention is an amountor quantity sufficient to increase the rate of ambient temperatureviscosity increase, gelation and hardening of the binder-aggregatematerial and such quantity can vary over a wide range depending on theactivity of the particular accelerator, the amount of accelerationdesired, the room or ambient temperature, the quantity of calcium oxidein the composition (generally as an impurity in the magnesia aggregate)and whether an ester hardening agent is also used. Thus the quantity ofaccelerator will generally vary from about 0.5% to 6% by weight of thephenolic resin, also referred to as "BOR".

Fillers, Aggregates and Modifiers

The compositions of this invention can include fillers, modifiers, andaggregates, in addition to the magnesia aggregate, such as those whichare conventionally used with phenolic resins. The additional aggregatematerial may be a particulate material such as that in granular, powder,or flake form. Suitable additional aggregate materials include but arenot limited to: alumina, zirconia, silica, zircon sand, olivine sand,silicon carbide, silicon nitride, boron nitride, bauxite, quartz,chromite, and corundum and mixtures thereof.

The binder-aggregate compositions produced by combining the curableresin binder, magnesia aggregate, and accelerator may additionallycomprise any of a number of optional modifiers or additives including:non-reactive solvents; silanes; hexamethylenetetraamine; clays;graphite; iron oxide; carbon pitch; silicon dioxide; metal powders suchas aluminum, magnesium, and silicon; surfactants; dispersants; airdetraining agents; and mixtures thereof.

Mixing of the ingredients for the binder-aggregate compositions of thisinvention may be accomplished in any means known in the art, i.e., usingany industrial mixer such as an Eirich mixer, a Simpson mixer , a Mullermixer, and the like. The binder aggregate mixture which results from themixing step may be molded by any technique known in the art andsubjected to pressure to form a desired shape. The binder in thebinder-magnesia aggregate composition will wet the aggregate so that thecomposition becomes shapeable or can fill out a mold such as byvibration. For example, the binder-aggregate may be subjected tocompression, isostatic pressing, transfer molding, extrusion, orinjection molding at desired temperatures and pressures. Followingshaping the shape may be permitted to harden at ambient temperature orit may be further hardened by thermally curing before or after ambienttemperature hardening. A typical heat treatment involves a continualincrease in temperature up to about 120° C. (248° F.) to 205° C. (400°F.) to effect thermal cure of the resin binder and evaporate off waterand organic solvent. Further heat treatment up to 800° C. to 1,000° C.further promotes carbonization of the resin binder.

The pH of the mixture comprising the phenolic resin, magnesia aggregateand accelerator will have a pH of at least 4.5 and depending on how longthe mixture has been prepared, a higher pH such as that of about 7 to10. The magnesia aggregate is basic and when the phenolic resin ormixture of phenolic resin and accelerator is acidic, the pH rises withtime and the resin solidifies at a pH above 7.

In order that those skilled in the art may more fully understand theinvention presented herein, the following procedures and examples areset forth. All parts and percentages in the examples, as well aselsewhere in this application, are by weight, unless otherwisespecifically stated.

RESIN CHARACTERIZATION

Resin B. This resole resin was prepared by charging a mole ratio offormaldehyde to phenol of 1.20 in the presence of an alkaline catalyst.Resin B had: a viscosity of 4,100 cps at 25° C.; a water content of 7.9%; a free phenol content of 14.6%; a solids content of 79%; anapproximate weight average molecular weight of 566, excluding the freephenol ; and a pH of 7.9.

Resin C. This resole resin was prepared by charging a mole ratio offormaldehyde to phenol of 1.25 in the presence of an alkaline catalyst.Resin C had the following properties: a viscosity of 3,000 cps at 25°C.; 7.6% of water; 13% of phenol; 78% solids ; an approximate weightaverage molecular weight, excluding the free phenol, of 406; and a pH of7.8.

Resin D. This resole resin was prepared by charging a mole ratio offormaldehyde to phenol of 1.25 in the presence of an alkaline catalyst.Resin D had the following properties: a viscosity of 3,000 cps at 25°C.; 9.7% of water; 11% of free phenol; 77% solids; an approximate weightaverage molecular weight of 536, excluding the free phenol; and a pH of7.9.

Preparation of Resin D. A solution of 3.621 kg (38.55 moles) of phenolwas reacted with 2.885 kg of 50% formalin (48.08 moles) and 38 g of 50%sodium hydroxide at 60°-75° C. over 50 minutes. The reaction was thenheated at 90°-92° C. for 40 minutes and then cooled to 60° C. at whichtime vacuum distillation was started at 26 inches of mercury.Approximately 31% of distillate was removed. The residue was heated at75° C. for several hours until a viscosity of 3,000 cps at 25° C. wasreached. This resin is further characterized above under the heading ofResin Characterization.

Preparation of Resin B. Resin B is prepared in much the same manner asResin D using a formaldehyde/phenol mole ratio of 1.20, but was advancedto a slightly higher molecular weight and higher viscosity atessentially equal solids.

Preparation of Resin E. This resole resin was prepared in a similarmanner to Resin B by replacing sodium hydroxide catalyst with 80 mole%of potassium hydroxide. Resin E had: a viscosity of 3900 cps at 25° C.;6.4% of water; 14% of free phenol; 79% solids; and approximate weightaverage molecular weight of 370 (including free phenol); and a pH of7.9.

PROCEDURE FOR DETERMINING EFFECT OF ADDITIVES ON QUALITATIVE FLOW OFPHENOLIC RESIN/MAGNESIA AGGREGATE MIXES

This procedure is also referred to as "Qualitative Flow Procedure".Glass vials (28 mm×57 mm) were charged with 5.0 g resin, additive andsolvent, if any, and after solution was effected, 4.0 g of the HighPurity magnesia or if specifically recited "Standard Grade" magnesia,which was mixed well for one minute with a spatula and then mixed foranother minute using an S/P Vortex Mixer of American Scientific Productsat a setting of 9-10. The term "High Purity" magnesia refers to powdered(to pass a 200 mesh U.S. Sieve Series screen) deadburned magnesia havinga 99+% content of MgO and 0.59 Ca % which, as CaO, amounts to 0.82% byweight. The term "Standard Grade" magnesia is used herein to describedeadburned magnesia containing about 92% of MgO and 2.48% CaO (I.77% Ca)by weight having the same particle size set forth for High Puritymagnesia. Relative viscosities of the mixes, with sets of 2 to 5 beingcompared simultaneously, were observed by laying at right angles, i.e.on their sides, at various intervals upon standing at room temperature(23°-25° C.). All mixes were quite fluid initially but generally becameimmobile and tack-free in 1 to 7 days. Immobile mixes were probed withan applicator stick to determine relative degree of tackiness whichrange from sticky initially, to taffy-like and then to tack-free (i.e.,the stick pulls out clean and free of resin). As the viscosity of afluid mix increases the mix becomes immobile. Further increases inviscosity are then shown by stickiness of the immobile mixture to theapplicator stick. Still further viscosity increase is evidenced by ataffy-like tackiness and an even more advanced viscosity is evidenced bywithdrawing the applicator stick clean and free of the mixture.Additionally, comparative viscosity increases were recorded, e.g., 3>2>1means that the viscosity of Mix 3 was higher or greater than (>) that ofMix 2 which in turn was greater than Mix 1. The use of more than onegreater than symbol "(>)" indicates a greater difference, i.e.,viscosity increase, as compared to the use of simply one "(>)" symbol.The mixtures which did not contain an additive are also referred to as"Controls".

EXAMPLE 1 EFFECT OF ACETIC ACID OR FORMIC ACID ADDITIVES ON QUALITATIVEFLOW OF RESIN C/HIGH PURITY MAGNESIA

This example was performed to test the comparative effect of acetic acidin Mix 2 and formic acid in Mix 3 in relation to the Control, Mix 1,which did not contain an additive. The tests were performed inaccordance with the hereinabove described Qualitative Flow Procedure.Each of the mixes contained 0.2 g of ethylene glycol and the quantity ofacetic acid or formic acid in each Mix was 0.06 g which is 1.2% based onthe weight of resin.

It can be seen from Table 1 that both acetic acid and formic acidaccelerate hardening and that formic acid was a more effective hardeneras compared to acetic acid. Use of the chemical equivalent of sodiumacetate in place of acetic acid or hardburned magnesia instead ofdeadburned magnesia in this example will produce similar results.

                  TABLE 1                                                         ______________________________________                                        EFFECT OF ACETIC ACID OR FORMIC ACID                                          ADDITIVES ON QUALITATIVE FLOW                                                 OF RESIN C/HIGH PURITY MAGNESIA                                               Hours       Order of Viscosity                                                Elapsed     Increase For the Various Mixes                                    ______________________________________                                         0.5-1      3>2>1                                                              3          3>2>>1                                                             5          3>>2>>1 Mix 1 is still quite fluid.                               24          3>2>>>1 Mix 1 is still fairly fluid.                              34          3 is non-tacky. Mix 2 is still tacky.                             47          Mix 1 is still flowable.                                          About 59    Mix 2 is non-tacky.                                               96          Mix 1 is slightly mobile, sticky.                                 ______________________________________                                    

EXAMPLE 2 EFFECT OF GLYCOLIC, LACTIC AND MALIC ACIDS ON QUALITATIVE FLOWOF RESIN C/HIGH PURITY MAGNESIA

This example was performed in accordance with the Qualitative FlowProcedure to test the comparative effect on viscosity of Mix 2 whichcontained glycolic acid (hydroxyacetic acid) at a concentration of 1.1%BOR; Mix 3 which contained lactic acid (2-hydroxypropionic acid) at 1.2%BOR ; and Mix 4 which contained malic acid (hydroxysuccinic acid) at1.2% BOR; in relation to Mix 1 which did not contain an additive.

It can be seen from Table 2 that glycolic and lactic acid enhanceviscosity increase, i.e., they acted as accelerators. Malic acid showsan apparent initial thixotropic effect but in reality retards viscosityincrease.

                  TABLE 2                                                         ______________________________________                                        EFFECT OF GLYCOLIC, LACTIC AND MALIC                                          ACIDS ON QUALITATIVE FLOW OF                                                  RESIN C/HIGH PURITY MAGNESIA                                                  Hours   Order of viscosity                                                    Elapsed Increase Of the Various Mixes                                         ______________________________________                                         1-6    4>>2>3>1                                                              23      2,4>>3>1                                                              24      2>3>>1>>>4 Mix 2 is immobile but still tacky.                                 Remixed all the samples after 24 hrs.                                 72      Mix 4 still shows flow                                                ______________________________________                                    

Following the procedure of Example 2 but using hardburned magnesia orStandard Grade magnesia instead of High Purity magnesia the glycolicacid will show its accelerating effect on the composition.

EXAMPLE 3 EFFECT OF ADIPIC ACID, SUCCINIC ACID AND 4-NITROPHENOL ON THEFLOW OF RESIN D/HIGH PURITY MAGNESIA

This example was performed in accordance with the Qualitative FlowProcedure to test the comparative effect of: Mix 2 containing adipicacid at a concentration of 1.6% BOR; Mix 3 containing succinic acid at aconcentration of 1.6% BOR; and Mix 4 containing 4-nitrophenol at aconcentration of 4% BOR; in relation to Mix 1 which did not containadditive.

The results of the tests in Example 3 are set forth in Table 3. It canbe seen from Table 3 that adipic acid, succinic acid and 4-nitrophenolact as viscosity accelerators. Similar results are obtained by use ofhardburned magnesia in place of the deadburned magnesia in this example.Also, acceleration results are shown by adding to Mix 2 10% BOR of gammabutyrolactone, propylene carbonate or triacetin.

                  TABLE 3                                                         ______________________________________                                        EFFECT OF ADIPIC ACID, SUCCINIC ACID AND                                      4-NITROPHENOL ON THE FLOW OF                                                  RESIN D/HIGH PURITY MAGNESIA MIXTURE                                          Hours  Order of Viscosity                                                     Expired                                                                              Increase for the Various Mixes                                         ______________________________________                                         1     2>3>4 which is equal or slightly greater than 1.                        4     2>3>4>1.                                                                6     Mix 2 moves very slowly.                                               23     Mixes 2 and 3 show no flow and are tack-free, Mix 1                           shows slight flow and-Mix 4 shows no flow but is not                          tack-free.                                                             47     Both Mixes 1 and 4 are tack-free but Mix 4 is                                 slightly firmer.                                                       ______________________________________                                    

EXAMPLE 4 EFFECT OF SALICYLALDEHYDE, SALICYLAMIDE AND 2-NITROPHENOL ONQUALITATIVE FLOW OF RESIN D/HIGH PURITY MAGNESIA

This example was performed to show changes in viscosity in accordancewith the Qualitative Flow Procedure described hereinabove with: Mix 2containing salicylaldehyde at a concentration of 4.4% BOR; Mix 3containing salicylamide at a concentration of 4.4% BOR; Mix 4 containing2-nitrophenol at a concentration of 4.4% BOR; and Mix 1 which was theControl and did not contain an additive. The results of the tests areshown in Table 4. It can be seen from Table 4 that after one day,salicylaldehyde and 2-nitrophenol increase mix viscosity relative to theControl and Salicylamide.

                  TABLE 4                                                         ______________________________________                                        EFFECT OF SALICYLALDEHYDE,                                                    SALICYLAMIDE AND 2-NITROPHENOL ON QUALI-                                      TATIVE FLOW OF RESIN D/HIGH PURITY MAGNESIA                                   Hours  Order of Increased                                                     Elapsed                                                                              Viscosity for the Various Mixes                                        ______________________________________                                         2.5-7 2>4>1,3                                                                23     2,4>1,3 Mixes 2 and 4 are essentially immobile but not                        tack-free. Mixes 1 and 3 move very slowly.                             48     All mixes are immobile and tack-free.                                  ______________________________________                                    

EXAMPLE 5 QUALITATIVE FLOW STUDIES OF RESIN B/HIGH PURITY MAGNESIA

This example was run in accordance with the Qualitative Flow Procedure.Results were noted of a control with no additives in comparison withsamples containing various additives, as set forth below. The testperiod lasted over a period of 5 days. It was observed that trimelliticacid (1,2,4-benzenetricarboxylic acid) additive at 1.0% BOR acted as amoderately effective accelerator. Sulfanilic acid(4-aminobenzenesulfonic acid) additive at a concentration of I.5% BORacted as a mild accelerator and aspartic acid additive at aconcentration of 1.5% BOR acted as a mild retarder. Use of the chemicalequivalent of potassium sulfanilate (the potassium salt of4-aminobezenesulfonic acid) or the chemical equivalent of ammoniumsulfanilate in place of sulfanilic acid will provide similar acceleratorresults.

EXAMPLE 6 EFFECT OF ADDITIVES ON FLOW OF RESIN B/HIGH PURITY MAGNESIA

This example was performed in accordance with the Qualitative FlowProcedure. In this example: Mix 1 is the control with no additive; Mix 2is phenolsulfonic acid at 1.4% BOR as the additive; Mix 3 is lithiumnitrate as the additive at 1 1% BOR; and Mix 4 contained ammoniumsulfamate as the additive at a concentration of 1.4% BOR. All the mixescontained 1.4% BOR of added water. The results of this example are shownbelow.

    ______________________________________                                        Hours     Order of Viscosity                                                  Elapsed   Increase For the Various Mixes                                      ______________________________________                                         0.5      4>2>3>1 where 4>>1                                                   1        4>>2 equal or slightly greater than 3>1                              2        4>>2 equal or slightly greater than 3>>1                                      Mix 3 was immobile while Mix 1 is quite fluid.                       3        4>2,3>>1 Mix 4 is tack-free.                                         9        3>2>>>1 Mix 1 still shows moderate flow.                            14        Mix 3 is close to tack-free but Mix 2 is not.                       21        Mixes 2 and 3 are tack-free.                                        31        Mix 1 still flows.                                                  48-72     Mix 1 is sticky.                                                    96        Mix 1 is tack-free.                                                 ______________________________________                                    

It can be seen from the results of Example 6 that: ammonium sulfamate isa powerful accelerator; and that phenolsulfonic acid and lithium nitrateare good accelerators. In an experiment run in a similar manner to theabove, acetylacetone (2,4-pentanedione) at a concentration of 2% BORshowed modest accelerator activity, i.e., less than that in the aboveExample 6. Use of the chemical equivalent of sodium sulfamate in placeof the ammonium sulfamate in this example as well as use of the chemicalequivalent of ammonium phenolsulfonate in place of phenolsulfonic acidor the chemical equivalent of potassium nitrate in place of lithiumnitrate will produce similar results.

EXAMPLE 7 EFFECT OF ADDITIVES ON FLOW OF RESIN E/HIGH PURITY MAGNESIA

This example was performed in accordance with the Qualitative FlowProcedure. Mix 1 was the control and did not contain an additive. Mix 2contained p-toluenesulfonic acid as the additive at a concentration of2% BOR. Mix 3 contained citric acid as the additive at a concentrationof 1.5% BOR plus N,N-dimethylethanolamine (DMEA) at a concentration of1% BOR. All of the mixes also contained an additional 1.4% BOR of water.The results of this example are shown below.

    ______________________________________                                        Hours  Order of Viscosity                                                     Elapsed                                                                              Increase For the Various Mixes                                         ______________________________________                                         0.66  3>2>1                                                                   1-5   3>2>1 with 3>>1 Mix 3 barely moves after                                      3-5 hours.                                                              6     Remixed after 6 hours and then 2>3>1.                                   14    3 equal or slightly greater than 2>>1.                                  24    2,3>>1 Mix 1 flows fairly easily. Remixed 1 and 3                             which were easily remixable whereas Mix 2 is too                              taffy-like to mix. After remixing 2 is equal or                               slightly greater than 1>>3 with mix 3 showing                                 good flow.                                                              26-33 2 equal or slightly greater than 1>>3. Mix 3 shows                            good flow whereas Mix 2 is not tack-free.                               39    2>1>>3. Mix 2 is just barely tack-free.                                 72    Mix 1 is still sticky, flowing very slowly. Mix 3                             still shows moderate flow which after remixing                                becomes good flow.                                                     127    Mix 1 is not tack-free and Mix 3 shows moderately                             good flow.                                                             144    Mix 1 is tack-free and Mix 3 shows moderately good                            flow.                                                                  288    Mix 3 flows before and after remixing.                                 336    Mix 3 still flows.                                                     ______________________________________                                    

The resin solution containing the retarder which was used to prepare Mix3 remained clear and homogeneous for at least 13 days.

It can be seen from the results of Example 7 that p-toluenesulfonic acidis an accelerator whereas citric acid/DMEA shows early thixotropy butbecomes a strong retarder. Use of the chemical equivalent ofbenzenesulfonic acid, naphthalenesulfonic acid or methanesulfonic acidin place of the p-toluenesulfonic acid will also show acceleration inhardening.

EXAMPLE 8 EFFECT OF ACCELERATOR USING RESOLE/NOVOLAC BLEND WITH HIGHPURITY MAGNESIA

Novolac A solution (65% solids with 25% furfuryl alcohol and 10% ethanoland a molecular weight of about 600 and having a viscosity of about 2170cps at 25° C.) can be mixed 1:1 by weight with Resin D to give aviscosity of about 2520 cps at 25°. This composition is tested withoutan additive as Mix 1 and with 2% BOR of ammonium toluenesulfonate as Mix2. These two Mixes are tested in accordance with the Qualitative FlowProcedure. Observation will show that the ammonium toluenesulfonateaccelerated the room temperature hardening of the composition inrelation to the composition which does not contain the ammoniumtoluenesulfonate.

EXAMPLE 9 EFFECT OF ACCELERATION ON QUALITATIVE FLOW WHEN USING NOVOLACALONE AS THE PHENOLIC RESIN WITH STANDARD GRADE MAGNESIA

This example shows the effect of an accelerator using a novolac resinwith Standard Grade deadburned magnesia but without a resole resin. Aphenol formaldehyde novolac resin is dissolved as a 60% solids solutionin ethylene glycol with about 3.5% water and a molecular weight of about3000 and a viscosity of about 5,700 cps at 25° C. The procedure used inthis example is the Qualitative Flow Procedure. The Standard Grademagnesia contained 2.5% of CaO. Mix 1 is the Control together with 0.6%of water BOR. Mix 2 contains 2% of ammonium sulfamate BOR. Observationwill show that the ammonium sulfamate accelerates the room temperaturehardening of the composition in relation to the composition which doesnot contain the accelerator.

EXAMPLE 10 EFFECT OF PHENOLSULFONIC ACID ON RESIN B

Resin B (50 g) was diluted with 1% water and then with very good mixingphenolsulfonic acid -(1.0 g, 65% active having 1.3% actives (BOR)gradually added. The resulting pH was 4.92 and the viscosity (25° C.)was 2970 centistokes. No apparent increase in viscosity was observedafter 3 days but a 14% increase was observed after 6 days.

It can be seen from Example 10 that the addition of 1.3% ofphenolsulfonic acid to Resin B at pH of 4.92 does not lead to observablehardening (i.e. viscosity increase) of the resin after several days at25° C. in the absence of the magnesia aggregate. In contrast to this,the similar formulation of Mix 2 in Example 6 which contained deadburnedmagnesia had solidified and was tack-free in 21 hours. Similar effectsas those of this example are expected with the use of Resin C or Resin Din place of Resin B or with other accelerators in place of phenolsufonicacid, provided that the pH of the resin is above 4.0.

What is claimed is:
 1. A method for accelerating the ambient temperaturehardening of a mixture of a phenolic resin and magnesia aggregatewherein the mixture has a pH of at least 4.5 which comprises mixing:A.magnesia aggregate; B. a curable phenolic resin solution selected fromthe group consisting of a novolac, a resole having a viscosity of about100 to 10,000 cps at 25° C., and mixtures thereof the quantity of saidresin being sufficient to bind the aggregate on thermal curing of theresin; and C. an accelerator compound in an amount sufficient toaccelerate the ambient temperature hardening of said mixture, saidcompound selected from the group consisting of: a compound whichprovides to the mixture 4-aminobenzenesufonate anions, acetylacetone,2-nitrophenol, 4-nitrophenol, salicylaldehyde; and a mixture of saidaccelerator compounds; provided however that the resin is a resole whenthe compound provides 4-aminobenzenesulfonate anions.
 2. The method ofclaim 1 wherein the aggregate is deadburned magnesia.
 3. The method ofclaim 1 wherein the aggregate is hardburned magnesia.
 4. The method ofclaim 1 wherein the resin is a resole resin having a pH of 5 to 8.5 anda viscosity of 250 to 5,000 cps at 25° C.
 5. The method of claim 1wherein the phenolic resin is the condensation product of phenol andformaldehyde.
 6. The method of claim 1 wherein the compound isacetylacetone.
 7. The method of claim 1 wherein the phenolic resin is asolution of novolac in an organic solvent and the aggregate containsfrom about 1.5% to 4% of calcium oxide.
 8. The method of claim 1 whereinthe phenolic resin is a mixture containing from about 1 to 4 parts byweight of resole for each part of novolac.
 9. The method of claim 1wherein the mixture includes an additive selected from the groupconsisting of from about 5% to 35% of graphite based on the weight ofaggregate, 1% to 5% by weight of a metal powder selected from the groupconsisting of aluminum, magnesium, and silicon based on the weight ofaggregate, and mixtures of said additives.
 10. The method of claim 1wherein the accelerator is salicylaldehyde.
 11. The method of claim 1wherein the accelerator provides 4-aminobenzenesulfonate anions.
 12. Themethod of claim 1 wherein the ambient temperature is from about 60° F.to 90° F.
 13. The method of claim 2 wherein the mixture includes fromabout 5% to 25% by weight, based on the weight of the resin, of an esterfunctional hardening agent selected from the group consisting of alactone, a carboxylic acid ester, a cyclic organic carbonate andmixtures thereof.
 14. The method of claim 4 wherein the resin has aviscosity of from about 250 to 5,000 cps at 25° C. and a solids contentof about 50% to 90% by weight, the mixture contains from about 3% to 12%by weight of water, the magnesia contains less than 3% by weight ofcalcium oxide, and the phenolic resole is the condensation product ofphenol and formaldehyde.
 15. The method of claim 4 wherein the resoleresin contains less than 1% by weight of sodium or potassium.
 16. Abinder-aggregate composition having a pH of at least 4.5 which comprisesa wet mixture of:A. magnesia aggregate; B. a curable phenolic resinsolution selected from the group consisting of a novolac, a resolehaving a viscosity of about 100 to 10,000 cps at 25° C., and mixturesthereof, the quantity of said resin being from about 3% to 15% by weightof the magnesia; and C. an accelerator compound in an amount sufficientto accelerate the ambient temperature hardening of said mixture, saidcompound selected from the group consisting of: a compound whichprovides to the mixture 4-aminobenzenesufonate anions, acetylacetone,2-nitrophenol, 4-nitrophenol, salicylaldehyde; and a mixture of saidaccelerator compounds; provided however that the phenolic resin is aresole when the compound provides 4-aminobenzenesulfonate anions. 17.The composition of claim 16 wherein the phenolic resin is a resolehaving a viscosity of 250 to 5,000 cps at 25° C. and wherein the resolecontains from 3% to 15% by weight of water.
 18. The composition of claim16 wherein the compound is acetylacetone.
 19. A binder-aggregatecomposition having a pH of at least 4.5 which comprises a wet mixtureof:A. magnesia aggregate; B. a curable phenolic resole resin solutionhaving a viscosity of about 100 to 10,000 cps at 25° C., the quantity ofsaid resin being from about 3% to 15% by weight of the magnesia; and C.a compound providing 4-aminobenzenesulfonate anions to the mixture in anamount sufficient to accelerate the ambient temperature hardening ofsaid mixture.
 20. The composition of claim 19 wherein the compoundproviding the resin is a resole.